1. Field of the Invention
The present invention relates to an insulated transformer and a power converting device, and is appropriately applied to a method using a glass substrate for insulating the primary winding and the secondary winding of the insulated transformer.
2. Background Art
In order to enhance the efficiency of, and to spare the energy consumption of, a modern vehicular device, a step-up/step-down converter and an inverter are mounted on a drive system for an electric motor to generate driving power. FIG. 9 is a block diagram showing a schematic arrangement of a vehicle driving system using a step-up/step-down converter according to the background art. In FIG. 9, the vehicle driving system is equipped with a power source 1101 for feeding electric power to a step-up/step-down converter 1102, for stepping a voltage up/down. An inverter 1103 of the system converts the voltage outputted from the step-up/step-down converter 1102 into a three-phase voltage. An electric motor 1104 drives the vehicle. The power source 1101 can be constituted of either a feed voltage from an aerial line or a battery connected in series.
When a vehicle is driven, the step-up/step-down converter 1102 steps up the voltage (e.g., 280 V) of the power source 1101 to a voltage (e.g., 750 V) suited for driving the electric motor 1104, and feeds the stepped-up voltage to the inverter 1103. By controlling the ON/OFF state of the switching element, the voltage stepped-up by the step-up/step-down converter 1102 is converted into a three-phase voltage so that the speed of the vehicle can be changed by feeding the electric current to the individual phases of the electric motor 1104, thereby to control the switching frequency.
When a vehicle brakes are applied, the inverter 1103 controls the ON/OFF state of the switching element in synchronism with the voltages arising in the individual phases of the electric motor 1104, so that it performs rectification to make a conversion into a DC voltage, thereby feeding the DC voltage to the step-up/step-down converter 1102. The step-up/step-down converter 1102 is enabled to perform power regeneration by dropping the voltage (e.g., 750 V) generated from the electric motor 1104, to the voltage (e.g., 280 V) of the power source 1101.
FIG. 10 is a block diagram schematically showing a constitution of the step-up/step-down converter of FIG. 9. In FIG. 10, the step-up/step-down converter 1102 is equipped with an inductor L for storing the energy; a condenser C thereof stores an electric charge, and switching elements SW1 and SW2 turn ON and OFF the electric current flowing into the inverter 1103. Control circuits 1111 and 1112 individually generate control signals to instruct turning the switching elements SW1 and SW2 ON and OFF.
The switching elements SW1 and SW2 are connected in series, and a node between SW1 and SW2 is connected with the power source 1101 through the inductor L. The switching element SW1 is equipped an IGBT (Insulated Gate Bipolar Transistor) 1105 for performing switching in accordance with control signals from the control circuit 1111, and a flywheel diode D1 for feeding the electric current in the direction opposed to that which the electric current flowing to the IGBT 1105 is connected in parallel with the IGBT 1105.
The switching element SW2 is equipped with an IGBT 1106 for performing switching actions in accordance with control signals from the control circuit 1112. A flywheel diode D2 feeding the electric current in the direction opposed to that of the electric current flowing to the IGBT 1106 is connected in parallel with the IGBT 1106. The collector of the IGBT 1106 is connected to both the condenser C and the inverter 1103.
FIG. 11 is a diagram showing a waveform of an electric current flowing through the inductor L of FIG. 10 in the stepping-up operation. In stepping-up, as shown in FIG. 11, when the IGBT 1105 of the switching element SW1 is turned ON (conductive), an electric current I flows through the IGBT 1105 to the inductor L so that an energy of LI2/2 is stored in the inductor L. Next, when the IGBT 1105 of the switching element SW1 is turned OFF (nonconductive), the electric current flows to the flywheel diode D2 of the switching element SW2, so that the energy stored in the inductor L is fed to the condenser C.
In the stepping-down action, when the IGBT 1106 of the switching element SW2 is turned ON (conductive), the electric current I flows to the inductor L through the IGBT 1106, so that an energy of LI2/2 is stored in the inductor L. Next, when the IGBT 1106 of the switching element SW2 is turned OFF (nonconductive), the electric current flows to the flywheel diode D1 of the switching element SW1, so that the energy stored in the inductor L is regenerated to the power source 1101.
By changing the ON time (ON Duty) of the switching element, the step-up/step-down voltage can be adjusted so that its rough value can be determined from the following formula (1):VL/VH=ON Duty (%)  (1).In formula (I) VL indicates the power source voltage, VH indicates the voltage after step-up/step-down, and ON Duty indicates the ratio of a conduction period to the switching period of the switching elements SW1 and SW2.
As a matter of fact, the load and the power source voltage VL fluctuate. Therefore, the voltage VH after step-up/step-down is monitored, and the ON time (ON Duty) of the switching elements SW1 and SW2 is controlled such that the step-up/step-down voltage VH may reach the target value. The control circuits 1111 and 1112 to be grounded to the body casing are on the low-voltage side, and the arm to be connected with the switching elements SW1 and SW2 is on the high-voltage side. In order that the human body may not be exposed to dangers even in the event of breakage of the switching elements SW1 and SW2, the signal transfer is made using a photocoupler to insulate the control circuits 1111 and 1112 electrically.
FIG. 12 is a block diagram schematically showing a constitution of an intelligent power module for the step-up/step-down converter of the background art. In FIG. 12, an intelligent power module for the step-up/step-down converter is equipped with switching elements SWU and SWD for turning ON/OFF an electric current flowing into loads, and a control circuit 1 for generating control signals to indicate the ON/OFF status of the switching elements SWU and SWD. The control circuit 1 can be constituted of a CPU 4 or a logical IC, or a system LSI having the logic IC and the CPU mounted thereon.
The switching elements SWU and SWD are connected in series so that they act for an upper arm 2 and a lower arm 3, respectively. The switching element SWU is equipped with an IGBT 6 for performing a switching action on the basis of a gate signal SU4. A flywheel diode DU1 is connected in parallel with the IGBT 6 for feeding an electric current inversely of the electric current flowing through the IGBT 6. The chip having the IGBT 6 is equipped with a temperature sensor using the VF change of a diode DU2 due to the temperature change of the chip as its measurement principle, and a current sensor for detecting a main circuit current by shunting the emitter current of the IGBT 6 through resistors RU1 and RU2.
The switching element SWD is equipped with an IGBT 5 for performing a switching action on the basis of a gate signal SD4. A flywheel diode DD1 is connected in parallel with the IGBT 5 for feeding an electric current inversely of the electric current flowing through the IGBT 5. The chip having the IGBT 5 is equipped with a temperature sensor and a current sensor. The temperature sensor uses the VF change of a diode DD2 due to the temperature change of the chip as its measurement principle. The current sensor detects a main circuit current by shunting the emitter current of the IGBT 5 through resistors RD1 and RD2.
The upper arm 2 is equipped with a gate driver IC 8 having a protecting function to generate the gate signal SU4 for driving the control terminal of the IGBT 6, while monitoring an overheating detection signal SU6 from the temperature sensor and an overcurrent detection signal SU5 from the current sensor. The upper arm also includes an analog PWM converter CU for generating a PWM signal corresponding to the temperature of the IGBT 6. The lower arm 3 is equipped with a gate driver IC 7 having a protecting function to generate the gate signal SD4 for driving the control terminal of the IGBT 5, while monitoring an overheating detection signal SD6 from the temperature sensor and an overcurrent detection signal SD5 from the current sensor. The lower arm also includes an analog PWM converter CD for generating a PWM signal corresponding to the temperature of the IGBT 5.
Photocouplers FU1 to FU3 and FD1 to FD3 are individually interposed between the side of the control circuit 1 to be grounded to the body casing and the upper arm 2 and the lower arm 3 to take a high voltage. These photo couplers are used to transfer the signals in the control circuit 1, while electrically insulating the side of the upper arm 2 and the side of the lower arm 3. On the side of the upper arm 2, specifically, a gate driver PWM signal SU1, as outputted from the CPU 4, is inputted through the photocoupler FU1 to the gate driver IC 8 with the protecting function. An alarm signal SU2, as outputted from the gate driver IC 8 with the protecting function, is inputted to the CPU 4 through photocoupler FU2. An IGBT chip temperature PWM signal SU3, as outputted from the analog PWM converter CU, is inputted to the CPU 4 through the photocoupler FU3.
On the side of the lower arm 3, a gate driver PWM signal SD1, as outputted from the CPU 4, is inputted through the photocoupler FD1 to the gate driver IC 7 with the protecting function. An alarm signal SD2, as outputted from the gate driver IC 7 with the protecting function, is inputted to the CPU 4 through the photocoupler FD2. An IGBT chip temperature PWM signal SD3, as outputted from the analog PWM converter CD, is inputted to the CPU 4 through the photocoupler FD3.
FIG. 13 is a block diagram showing a schematic constitution of a peripheral circuit of the photocoupler. In FIG. 13, a photocoupler 2008 is equipped with an infrared light emitting diode 2003 for emitting an infrared light with a forward current If. A light receiving diode 2004 of the photocoupler receives the emitted infrared light, and a bipolar transistor 2005 performs a current amplifying action by using a photocurrent generated in the light receiving diode 2004, as its base current. The infrared light emitting diode 2003 has its cathode connected with a field effect type transistor 2001 through a resistor 2002, and the bipolar transistor 2005 has its collector connected with a power voltage Vcc2 through a resistor 2006. An output signal Vout, as outputted through the collector of the bipolar transistor 2005, is inputted to an IGBT drive IC 2007.
When a signal SP is inputted to the gate of the field effect type transistor 2001, the forward current If flows to the infrared light emitting diode 2003 so that the infrared light is emitted. The infrared light emitted from the infrared light emitting diode 2003 is received by the light receiving diode 2004 so that a photocurrent according to the infrared light flows to the base of the bipolar transistor 2005. When the photocurrent flows to the base of the bipolar transistor 2005, a collector current Ic flows to the bipolar transistor 2005. When the collector current Ic flows to the resistor 2006 connected at its one end with the power voltage Vcc2, the change in the voltage at the other end of the resistor 2006 is inputted as the output signal Vout to the IGBT drive IC 2007.
The input/output characteristics of the single photocoupler 2008 can be defined by a current transfer ratio (CTR), i.e., Ic/If. When the circuit is designed using the photocoupler 2008, the following points have to be considered: (1) the temperature characteristics of a current amplification factor hfe of the bipolar transistor 2005; (2) the lifetime deterioration of the light emitting efficiency of the infrared light emitting diode 2003; and (3) the dispersion of the CTR.
FIG. 14 is a diagram showing the temperature characteristics of the current transfer efficiency of the photocoupler. In FIG. 14, the current transfer efficiency of the photocoupler 2008 becomes is reduced as the temperature becomes is reduced. This is caused by the temperature characteristics of the current amplification factor hfe of the bipolar transistor 2005. FIG. 15 is a diagram showing deterioration due to age characteristics of the current transfer efficiency of the photocoupler. In FIG. 15, the CTR of the photocoupler 2008 drops in dependence upon the forward current, the environmental temperature and the accumulated usage time of the light emitting diode 2003. The drop of the CTR appears prominently when the continuous usage time of the photocoupler 2008 exceeds 1,000 hours.
FIG. 16 is a diagram showing the dispersion of the current transfer efficiency of the photocoupler. In FIG. 16, the current transfer efficiency of the photocoupler is highly dispersed. This is caused by the dispersion of the light emitting efficiency of the light emitting diode 2003 or the current amplification factor hfe of the bipolar transistor 2005. Where the photocoupler is used as insulation transfer means in the intelligent power module for the step-up/step-down converter of FIG. 12, the circuit design has to be made considering the aforementioned points. Continuous use over more than 10 years is difficult in the hot atmosphere of a vehicle or an industrial device. An insulated transformer may be used as the transfer signal insulating means instead of the photocoupler. A micro-transformer that may be used as this insulated transformer, which can be drastically miniaturized by utilizing MEMS (Micro Electro Mechanical Systems) techniques, has been produced by several makers.
FIG. 17A is a sectional view showing a schematic arrangement of the insulated transformer of the background art, and FIG. 17B is a top plan view showing the schematic arrangement of the insulated transformer of FIG. 17A. In FIG. 17, an outgoing wiring layer 12 is buried in a semiconductor substrate 11, and a primary coil pattern 14 is formed over the semiconductor substrate 11. The primary coil pattern 14 is connected with the outgoing wiring layer 12 through an outgoing portion 13. A flattened film 15 is formed over the primary coil pattern 14, and a secondary coil pattern 17 is formed over the flattened film 15, which is covered with a protecting film 18. An opening 19 is formed in the protecting film 18 for exposing the center of the secondary coil pattern 17 to the outside. The outgoing wiring from the secondary coil pattern 17 can be made by connecting a bonding wire to the center of the secondary coil pattern 17 through the opening 19. The primary coil pattern 14 and the secondary coil pattern 17 can have a winding width of 5 to 10 μm, a thickness of 4 to 5 μm and the outermost winding diameter of 500 μm, for example.
FIG. 18 and FIG. 19 present sectional views showing methods for manufacturing the insulated transformer of the background art. In FIG. 18A, an impurity such as As, P or B is selectively injected into the semiconductor substrate 51, thereby forming such an outgoing diffusion layer 52 in the semiconductor substrate 51 as is led out from the center of the primary coil pattern 55a. The material for the semiconductor substrate 51 can be selected from Si, Ge, SiGe, SiC, SiSn, PbS, GaAs, InP, GaP, GaN or ZnSe.
Next, the insulating layer 53 is formed by the plasma CVD method or the like on the semiconductor substrate 51 having the outgoing diffusion layer 52 formed therein, as shown in FIG. 18B. The material for the insulating layer 53 can be exemplified by a silicon oxide film or a silicon nitride film. Next, as shown in FIG. 18C, by using the photolithography technique, a resist pattern 54, which has an opening 54a formed to correspond to the outgoing portion from the center of the primary coil pattern 55a, is formed over the insulating layer 53. Next, as shown in FIG. 18D, the insulating layer 53 is etched by using the resist pattern 54 having the opening 54a as the mask, so as to form such an opening 53a in the insulating layer 53 to correspond to the outgoing portion from the center of the primary coil pattern 55a. Next, as shown in FIG. 18E, the resist pattern 54 is peeled off from the insulating layer 53 by means of chemicals.
Next, as shown in FIG. 18F, a conductive film 55 is formed over the insulating layer 53 by a sputtering or vapor deposition method. The material for the conductive film 55 can be exemplified by a metal such as Al or Cu. Next, as shown in FIG. 18G, a resist pattern 56 corresponding to the primary coil pattern 55a is formed by using the photolithography technique. Next, as shown in FIG. 18H, the primary coil pattern 55a is formed over the insulating layer 53 by etching the conductive film 55, using the resist pattern 56 as a mask. Then, as shown in FIG. 18I, the resist pattern 56 is peeled off from the primary coil pattern 55a by means of chemicals.
Next, as shown in FIG. 18J, a flattened film 57 is formed by the plasma CVD method or the like over the insulating layer 53 having the primary coil pattern 55a. The material for the flattened film 57 can be exemplified by the silicon oxide film or the silicon nitride film. Then, as shown in FIG. 18K, the flattened film 57 is flattened and cleared of its surface roughness by an oblique etching method or CMP (Chemical Mechanical Polishing) method. Next, as shown in FIG. 18L, by using the photolithography technique, a resist pattern 58, which has an opening 58a formed to correspond to the wiring outgoing portion of the outer end of the secondary coil pattern 60a, is formed over the flattened film 57.
Next, as shown in FIG. 19A, the flattened film 57 is etched by using the resist pattern 58 having the opening 58a as a mask, forming an opening 57a corresponding to the wiring outgoing portion of the outer end of the secondary coil pattern 60a over the flattened film 57. Next, as shown in FIG. 19B, the resist pattern 58 is peeled off from the flattened film 57 by means of chemicals. Next, as shown in FIG. 19C, a separating layer 59 for the primary coil pattern 55a and the secondary coil pattern 60a is formed over the flattened film 57. The method for forming the separating layer 59 can be exemplified by the method for forming a polyimide layer over the flattened film 57 by a spin coating. Alternatively, the separating layer 59 may also be formed by forming a silicon oxide film over the flattened film 57 by the sputtering method.
Next, as shown in FIG. 19D, a conductive film 60 is formed over the separating layer 59 by the sputtering or vapor deposition method. The material for the conductive film 60 can be exemplified by a metal such as Al or Cu. Next, as shown in FIG. 19E, a resist pattern 61 corresponding to the secondary coil pattern 60a is formed by using the photolithography technique. Next, as shown in FIG. 19F, the conductive film 60 is etched by using the resist pattern 61 as a mask, thereby forming the secondary coil pattern 60a over the separating layer 59. Next, as shown in FIG. 19G, the resist pattern 61 is peeled off from the secondary coil pattern 60a by means of chemicals.
Next, as shown in FIG. 19H, a protecting film 62 is formed over the separating layer 59 having the secondary coil pattern 60a, by the plasma CVD method. The material for the protecting film 62 can be exemplified by a silicon oxide film or a silicon nitride film. The protecting film 62 is patterned by using the photolithography technique and the etching technique, to expose the end portions and the central portions of the secondary coil pattern 60a to the outside.
In JP 2005-5685 A (corresponding to U.S. Pat. No. 6,927,664), for example, a method is disclosed for reducing the occupied area of a transformer element formed of a first wiring layer and a second wiring layer. When one of the first wiring layer and the second wiring layer is projected from one of the vertically upward direction and the vertically downward direction, a contour projected has a symmetrical shape with reference to a predetermined reference plane. The portion in which the projected contour might otherwise interlink over one of the first wiring layer and the second wiring layer is made not to interlink by using the first wiring layer and the second wiring layer.
In US 2005/0230837 A1, for example, an air-core transformer is disclosed that is equipped with first and second coils enclosed in the horizontal direction by a protecting ring. In JP 2005-310959 A, for example, a method is disclosed in which a laminated transformer is constituted from a magnetic sheet having coil conductors individually formed on its surface, and a magnetic sheet having glass insulating layers individually formed on its surface, so that the insulating withstand voltage between the coils is raised without increasing the height of the parts, while suppressing the reduction in coupling between the coils of the laminated transformer.